1. Field of the Invention
The present invention relates in general to an apparatus for monitoring a condenser for its corrosion resistance and condition of contamination, and more particularly to an apparatus for monitoring a condenser wherein a coolant such as seawater or estuary water is caused to flow through condenser tubes made of a copper alloy, and which is equipped with a ferrous-ion injecting device for injecting ferrous ions into the coolant, which is passed through the condenser tubes, in order to form a protective film on the inner surface of the condenser tubes, and a sponge-ball supply device for introducing sponge balls into the condenser tubes for removing deposits inside the tubes.
2. Discussion of the Prior Art and its Problems
As heat exchange condenser tubes for condensers in thermoelectric or steam power plants, chemical plants, or vessels or ships, there have been widely used special aluminum brass tubes having a composition which consists of brass as a base material, aluminum, arsenic, and other additives such as silicon, or alternatively, copper-alloy tubes such as cupronickel tubes made of copper, nickel, iron and manganese are used as the condenser tubes. Such condensers are adapted such that a coolant such as seawater (interpreted to include bay or estuary water) flows through the condenser tubes, while a high-temperature fluid (usually in its vapor phase) contacts the outer surface of the condenser tubes, whereby a heat exchange occurs beween the coolant and the hot fluid, via the condenser tubes. Since seawater is typically used as the coolant, the condenser tubes suffer from contamination or fouling during a long period of service, due to deposits of various substances on the inner surfaces of the tubes. These substances differ depending upon the nature of the specific seawater used. For example, the inner surfaces of the condenser tubes are subject to deposition of mud and sand or other sludges, iron rusts, corrosion products, and slime. These foreign substances reduce the overall heat transfer coefficient (thermal conduction characteristics) of the condenser tubes, thereby deteriorating the thermal efficiency of the condenser.
In light of the above, the maintenance of the copper alloy condenser tubes of a condenser wherein seawater is used as a coolant has been conventionally accomplished by (a) preventing corrosion of the inner surface of the tubes by the cooling seawater, and (b) preventing deposition or accumulation of various suspended matters and corrosion products on the inner surface of the tubes, and thus avoiding the deterioration of thermal conduction characteristics of the tubes. Described more specifically, it has been found extremely effective to inject ferrous ions in the form of ferrous sulfate into the coolant for protecting the condenser tubes, and to use sponge balls for cleaning the inner surface of the tubes to remove the deposited matters.
While the corrosion resistance of the condenser tubes is remarkably improved by a protective film of ferric hydroxide formed of ferrous ions as a result of injection of ferrous sulfate, for example, it is also known that such a protective film will reduce the thermal conduction characteristics of the condenser tubes. On the other hand, the cleaning of the condenser tubes with sponge balls results in enhancing the heat transfer rate of the tubes, but at the same time may cause a decline in the corrosion resistance of the tubes, if the protective film on the inner tube surface is excessively removed by the sponge-ball cleaning. Thus, there is a general recognition that the ferrous-ion injection and the sponge-ball cleaning are not satisfactorily stable and reliable for maintaining the required corrosion resistance and heat transfer characteristics of the condenser tubes.
In view of the above drawbacks, it has been proposed to inject ferrous ions and introduce sponge balls into the condenser tubes, according to a program which is predetermined based on laboratory tests or field tests, so as to satisfy the two requirements, i.e., corrosion resistance and heat transfer rate of the condenser tubes. The program to carry out the ferrous-ion injection and sponge-ball cleaning is modified or revised as needed, based on the results of periodic inspection of the condenser tubes. Since the nature of the cooling seawater, when used as the coolant is not kept constant during the service of the condenser, i.e., may be considerably varied, the ferrous-ion injection and sponge-ball cleaning according to the predetermined program have not been proved satisfactory for all operating conditions of the condenser, in maintaining the optimum corrosion resistance and heat transfer characteristics of the condenser tubes.
Another method of controlling the ferrous-ion injecting and sponge-ball cleaning operations is to monitor the corrosion resistance and heat transfer characteristics of the condenser tubes by directly measuring the polarization resistance of the condenser tubes which represents the corrosion resistance, and by sensing the cleanliness factor of the inner tube surfaces which represents the heat transfer rate. According to this method, devices for injecting ferrous ions and introducing sponge balls are controlled based on changes in the continuously measured or sensed polarization resistance and cleanliness factor. However, this proposed monitoring method is not practically available, since it has the following drawbacks, in relation to the position of installation of measuring or sensing devices, or the sensing arrangement.
In measuring or detecting the polarization resistance, a measuring device is installed within a water chamber of the condenser. This means that the measured polarization resistance is that of the condenser tubes at their ends open to the water chamber. Therefore, if the condenser tubes are long, for example, 10 m or more, the measurement does not exactly represent the polarization resistance at the substantive portion of the condenser tubes. Further, the measurement is influenced by the polarization resistance of a tube plate disposed to support the condenser tubes at the above-indicated end. Furthermore, the above measuring it made under cathodic protection, and therefore does not permit accurate detection of the polarization width, if the natural potential is fluctuated. Moreover, since the condenser uses thousands or ten thousands of condenser tubes, there exists a problem of difficulty to evaluate the measured polarization resistance, in relation to a variation in the actual conditions of these numerous condenser tubes.
Regardless of whether the heat transfer rate of the condenser tubes are evaluated by the cleanliness factor of the inner tube surfaces or by a value of vacuum or reduced pressure outside the tubes, the obtained measurements are affected by various variables associated with the water vapor introduced into the condenser, for example, humidity, flow condition and amount of air of the vapor stream. Namely, the measured cleanliness factor or vacuum represents that of the condenser as a whole, and never represents the contamination or fouling of the inner surfaces of the condenser tubes. Therefore, the ferrous-ion injection and sponge-ball cleaning based on the obtained measurements will not result in establishing optimum conditions of the tubes. It is also noted that there are differences among the numerous condenser tubes, in the flow rate of the cooling water and the number of the sponge balls passed. Thus, the conventional method tends to suffer from inaccuracy of evaluation of the cleanliness factor of each individual condenser tube.
As described above, the condenser has many factors that make it difficult to achieve accurate detection of the cleanliness factor or vacuum indicative of the heat transfer characteristics of the condenser tubes: variations among the large number of copper alloy condenser tubes, as many as several thousands to several ten thousands, including differences in the flow rate of the coolant, formation of a protective film (iron layer), number of the sponge balls passed, and magnitude of electrolytic potential; and variations in the longitudinal direction of the condenser tubes which may be as long as 20 m or even more. In addition, the condenser tubes are exposed to different conditions of the water vapor at their outer surfaces, and other different environmental factors. All of the above-indicated variables will influence the obtained meaurements of the cleanliness factor or vacuum, lowering the accuracy or reliability of estimation of the heat transfer characteristics of the condenser tubes. Even if the accuracy of the sensing device itself is satisfactory, the conventional monitoring method is not practical for the various factors described above.